“…On the other hand, the rapid development of optical and piezoelectric application urgently calls for environment-friendly materials substituting for lead-based systems [2,3]. Currently, leadfree piezoelectric materials that have been intensively studied including Bi 0.5 Na 0.5 TiO 3 -based materials [4][5][6], bi-layered structure materials [7][8][9], tungsten bronze-type materials [10] and alkaline niobate-based materials [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26].…”